1. Field of the Invention
This invention relates generally to light emitting diodes (LEDs) and more specifically to LEDs mounted on rigid circuit boards with an integrated aluminum heat sink where the circuit boards are frangible and also include the heat sink as an integrated element.
2. Background Art
Light emitting diode (LED) lamps are replacing incandescent lamps because of lower energy consumption, increased efficiency and longer lifetimes of the lamps. Low-intensity LEDs can provide efficient luminosity without requiring excessively large heat sinks. For low power LEDs, heat can be dissipated through multi-layered printed circuit board. The heat dissipation therethrough is normally sufficient to keep the LED junction temperature under the maximum rated value set by the manufacturer. However, increasing power and LED intensity requires an external sink for dissipating heat which cannot be adequately channeled through the printed circuit board and lamp base.
With mounting of LEDs in large arrays to provide increasing luminosity, use of numerous densely packed LEDs becomes increasingly difficult because of the need to provide large heat sinks to remove heat, without detracting from the appearance of the lamps and avoiding possibly blocking some of the emitted light. The self contained nature of LEDs, which are usually powered through electronic circuits having an outside power source, require that the heat sink efficiently remove heat from the circuits and from the LED itself. Especially when higher intensity LED lamps are used, the heat dissipation requirements increase and heat sinking properties of various thermally conductive materials have been relied on in providing the heat sink capacity for concentrated arrays of LEDs.
Thermal management of high power LEDs is generating intense scrutiny in the field. Since common FR4 circuit boards do not provide a high level of heat dissipation, it has been found that aluminum is a good heat sink material. For example, described in U.S. Pat. No. 7,1921,55, an aluminum base plate is used for mounting LEDs. This type of heat sink removes heat from the integrated circuits associated with the LEDs and acts to transfer the heat from the base to an outer housing which acts as the external heat sink for removing heat.
It has also been found desirable in the manufacture of LED arrays to provide circuitry that is capable of being subdivided by manual methods without affecting the ability to connect the underlying circuitry to a source of power and to control mechanisms. In U.S. Published Patent Application No. 2013/0083533 to Janik et al., proposes to use a base for an array of LEDs that is frangible so that it can be folded into a space for use in a lamp that resembles in form a normal incandescent bulb. Janik et al. propose for dissipating heat in higher intensity LED lamps, individual LEDs mounted on a thermally conductive medium, such as an aluminum plate. However, mounting LEDs on a plate of even nominal thickness will reduce the view angle of the emitted light, resulting in a noticeable band of lower intensity light when projected on a nearby surface. Thus, the need for a frangible board that permits the folding into a configuration that fits into the space available.
Another method use of an array of LEDs is in a line array along a strip or elongated fixture which has a variable length. Architectural lighting applications call for long, seamless linear lighting fixtures that may be visible in plain sight. Some products available in the form of FR4 fiberglass/epoxy rigid circuit boards can be manufactured in varying lengths and can be assembled with soldered pins in an additive fashion to make the arrays in desirable lengths. This type of rigid light engine assembly is sometimes prone to connection failures between the sections due to shock or vibration in transit during installation and through rugged use. An increase in labor time and costs for assembly results in many instances because the junctions must be soldered by hand. The many solder junctions and mechanical electrical connections can also create a weak point in the circuit. Metal linear fixtures may expand and contract as the light array warms up and cools down, fatiguing solder joints over time and causing premature failures as well as other problems with noise and ingress protection.
A linear array should ideally be suitable for direct view applications (diffused light versus pixelation or ‘dots’), and should also be able to be cut to desired lengths to fit millwork, coves, shelving, etc. so as to mitigate the appearance of dead spots without light. Thin, flexible circuit boards are currently employed for these applications. So called “tape lights,” in which strips of somewhat flexible tape on which LEDs are mounted, serve this function, but several drawbacks exist with such use. Among these are the inability to adequately remove heat from mid-power LEDs because these flexible materials, although allowing to be cut to a desired size by, for example scissors, the heat sink capabilities of such flexible tape materials remain wanting. The requirement for a fit to size linear array heretofore has not been addressed in the context of high intensity LED arrays that generate a significant amount of heat so as to impair the operation of the devices with continuous use. What is needed is a variable length, frangible linear LED heat sink with circuit board manufacturing techniques that is made from aluminum or other rigid heat sink material.